Charlatans epitomize the well known Human phrase, "Jack of all trades, master of none." Their legitimate talents are few and far between, but they strive to appear masterful at many arts. In truth, the only art in which Charlatans excel is that of deception. This mastery of deceit enables them to dupe others into believing that they possess more power and knowledge than they do. As a result, Charlatans are frequently found leading human populations, though usually in the guise of being a "servant of the people."
Charlatans are merely competent in both fighting and magic. Their ability to ruthlessly exploit an opponent's weaknesses makes them a genuine threat to all races. They often use stealth and deception to create and seize "unfair" advantages. The most legendary Charlatans are often given the nickname of "Slick," "Slimy," or "More slippery than a Lizardman."
Charlatans are a bit of a gamble as far as unit investments go. While Cavaliers are the more obviously important choice for Level 3 Human units, Charlatans can provide the Humans with interesting and unique strategic advantages in some situations.
With their bard's skills ability, shared only by the Halfling Satyr among regular units, a Charlatan can keep any unit of almost any race (except possibly the Undead) happy as long as you can capture a city and produce it. Notably, having multiple units with bard's skills in the same party causes the effect to stack, boosting the morale of even hostile units to manageable levels, although having such an abundance of Charlatans just to appease a few enemy units would be a questionable strategy.
This is even more significant for Humans than for the Halflings since Humans are of neutral alignment and thus do not have terrible relations with any one race by default, meaning only one Charlatan should be needed in an army to prevent almost any unit from deserting. On top of that, a Charlatan can use charm to attempt to gain control of any enemy unit in battle, though this will not always work and will give the unit a free attack if it doesn't.
Aside from that they are a little underwhelming, with concealment being only a little useful without also having the ability to scale walls, and magic bolts being a mediocre ranged attack at best. Charlatans are not too hard to deal with when fighting them, since they have fairly unimpressive combat stats. As long as you don't just send one unit with low Resistance against them to be charmed, you should be fine.